> the most important missing feature at the time was that to doesn't show other user's selections unlike many other collaboration tools. That means what you see is not what you're collaborators see. If you grab some shapes they don't see that you grabbed them.

This should work out of the box if you're collaborating. But, we've recently upgraded our collaboration servers and due to ServiceWorker caching it may be your colleague (or you) were connecting to the old one. Try hard refresh your browser.